The present invention relates to apparatus for the draining of accumulated moisture from the air pressure system of vehicles and, more particularly, to apparatus for periodically draining the moisture automatically.
A common form of braking system in large trucks is a type which operates utilizing air pressure. The truck engine operates an air compressor which provides the pressure for the braking system. The air pressure is stored generally in a pressure storage tank appropriately located within the vehicle in order that a constant pressure supply may be available.
During operation of the air compressor, air is pulled from the atmosphere and compressed by the air compressor. Atmospheric air contains moisture which, upon compression, causes the moisture to condense. Throughout continued use of the pressure system, the moisture will build up in the form of liquid in the pressure storage tank.
Continued presence of moisture in the air brake system can cause considerable harm to the system and even brake failure. For example, the moisture can cause deterioration of rubber seals and the like. Additionally, in cold weather, where the moisture has migrated into the pressure lines and other aspects of the braking system, it can freeze causing malfunction or total failure of the braking system.
For the foregoing reasons, it is essential that the moisture, which eventually accumulates in the pressure storage tank, be drained from the tank before it builds to a level to migrate into the remainder of the braking system. A conventional means for removing moisture from the braking system and, more particularly, from the pressure storage tank is to utilize a separate tank positioned adjacent to the pressure storage tank and interconnected with the pressure storage tank by means of a check valve. This separate tank, known as a wet tank, will collect the liquid or moisture in a manner well known in the art.
During normal operation, the wet tank, which has a drain valve in the bottom thereof, operates with the drain valve closed thereby allowing moisture to accumulate therein. Periodically and usually at the end of every day when the vehicle is shut down, the drain valve on the wet tank is manually opened. The check valve between the pressure storage tank and wet tank will then go into a closed position and the moisture which has accumulated in the wet tank, by means of the pressure already present therein, will blow the moisture out of the wet tank and purge the system.
The foregoing system for draining of moisture from the air braking system of a vehicle, if operated properly, will be effective. However, one of the severe drawbacks of such a system is that the operators of the vehicle forget to drain the wet tank. After a period of time, the wet tank will fill and the moisture will enter the pressure storage tank and ultimately the remainder of the system with grave consequences.
What is needed in the industry is a means by which the wet tank can be periodically drained automatically. Equally important, however, is that such an automatic draining system be of the type and nature that a failure of the system to drain will work in a fail-safe mode, i.e. upon a failure of the drain system to work automatically, pressure will not be released from the pressure system which would, of course, render the braking system inoperative and thus create a dangerous situation.
Applicant's prior U.S. Pat. No. 4,928,724 proposed a system for accomplishing this result by providing an arrangement which automatically drained accumulated moisture from the wet tank whenever the vehicle was placed in a shutdown mode. That is, an electrically operated solenoid opened a valve each time that the ignition key to the vehicle was turned off. While this system was an advance over prior art manual systems, it also suffered from several deficiencies.
One major deficiency of the prior art patented system was its cost. The combination of the pressure activated valve and solenoid made the arrangement somewhat costly and also more difficult to install. A more serious problem, however, was the prior system's inability to accomplish its desired result under certain conditions.
It is common practice for truck drivers during long cold trips to never turn their truck off. When taking a break or stopping for a meal, a truck driver frequently leaves the engine running. It would not be uncommon for the engine to run for 10, 12 or 14 hours continuously without ever being shut off. Since applicant's prior patented system drained the wet tank only during shutdown of the vehicle, the wet tank would not be drained during the entire 12- or 14-hour period that the truck was running. This creates particularly serious problems during very cold weather which is also the type of weather wherein a truck driver tends to leave the engine running.
Prior U.S. Pat. No. 3,101,091 to Schultz also proposes a system which is intended to automatically discharge accumulated moisture in the air compressor system of a vehicle. The Schultz system includes a pressure-activated valve which has a reservoir contained therein which is capable of holding a small amount of accumulated moisture and air. This valve is actuated every time the truck's brakes are depressed. While the Schultz system may have some advantages over other prior systems, it is capable of removing only a very small amount of moisture each time that it is activated and it can be more easily worn since it is activated so frequently. Furthermore, should a defect occur in the Schultz device, the entire braking system of the truck can be jeopardized.